The present application relates to battery chargers.
Recent years have seen a proliferation of battery powered electrical devices. Digital cameras, personal digital assistants (PDAs), hand held games, portable audio players, remote control devices, wireless computer keyboards and mice, and mobile telephones are but a few examples of this trend.
Rechargeable (secondary) batteries, such as nickel-metal hydride (NiMH), nickel-cadmium (NiCd), and lithium ion (LiIon) electrical cells, have likewise gained increasing acceptance as a renewable power source for these and other devices. Rechargeable batteries are typically well-suited for use in relatively high-drain devices, making them attractive in a wide variety of applications. As they can be recharged and reused, rechargeable batteries can also provide convenience and cost advantages relative to non-rechargeable (primary) batteries.
Another trend has been the widespread adoption of the universal serial bus (USB) interface standard. USB ports have become commonplace on personal computers (PCs) such as the so-called “Wintel,” Apple Macintosh, and various handheld and laptop computers, with some such PCs containing as many as six (6) or more USB ports. These ports provide bidirectional digital communications functionality and are often used for connecting mice, keyboards, game pads, joysticks, scanners, digital cameras, printers, and other peripheral devices which communicate with a PC.
Devices which exploit the power supply capabilities of USB ports have also been developed. Examples have included USB powered coffee mug warmers, fans, lights, and other devices which do not otherwise utilize the data communication capabilities afforded by the USB standard. Another example of these devices has been USB powered battery chargers. Unfortunately, however, these types of USB powered devices are not USB compliant and, depending on their current draw, may not work with USB compliant ports. In the case of USB powered battery chargers, charging performance may also be compromised.
A USB powered battery charger is also disclosed in U.S. Pat. No. 6,507,172 to Sherman, issued Jan. 14, 2003 and entitled Universal Serial Bus Powered Battery Charger. According to Sherman, the battery charger is intended primarily for use in battery powered hand-held and other devices to charge the battery or batteries within the battery powered device when the device is connected to a host device, powered hub, or a bus powered hub through a USB port. The charger also includes one or more current limits to conform to the USB current supply limit set in the USB specification. More specifically, the charger is incorporated into a system which determines the current capability of the host or powered hub by polling the USB host to determine if the USB is capable of providing 500 milliamps or only 100 milliamps. The battery charging current is selected accordingly.
While such a battery charger may provide certain performance advantages as compared to chargers which do not utilize the communications capabilities afforded by the USB standard, there nonetheless remains room for improvement.